Field-effect transistor including a metal oxide composite protective layer, and display element, image display device, and system including the field-effect transistor

ABSTRACT

To provide a field-effect transistor, containing: a substrate; a protective layer; a gate insulating layer formed between the substrate and the protective layer; a source electrode and a drain electrode, which are formed to be in contact with the gate insulating layer; a semiconductor layer, which is formed at least between the source electrode and the drain electrode, and is in contact with the gate insulating layer, the source electrode, and the drain electrode; and a gate electrode, which is formed at an opposite side to the side where the semiconductor layer is provided, with the gate insulating layer being between the gate electrode and the semiconductor layer, and is in contact with the gate insulating layer, wherein the protective layer contains a metal oxide composite, which contains at least Si and alkaline earth metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/440,969 filed May 6, 2015, the entire contents of which isincorporated herein by reference. U.S. application Ser. No. 14/440,969is a 371 of International Application No. PCT/JP2013/082512 filed Nov.27, 2013, and claims the benefit of priority from prior JapaneseApplication No. 2012-262079 filed Nov. 30, 2012.

TECHNICAL FIELD

The present invention relates to a field-effect transistor, a displayelement, an image display device, and a system.

BACKGROUND ART

A field-effect transistor (FET), which is a type of semiconductordevices, is a transistor configured to apply gate voltage to excite acarrier in a semiconductor in a state that an electric field is appliedto a channel so that electric current passed through between a sourceand a drain can be controlled.

Since the FET is capable of switching by applying gate electrode, theFET is used as various switching elements, or amplifier elements. As theFET has a flat structure as well as using low gate electric current, theFET can be easily produced compared to a bipolar transistor. Moreover,high integration of the FET can be also easily carried out. For thesereasons, the FET has been used in many of integrated circuits of currentelectric devices.

Among them, the FET is applied as a thin film transistor (TFT) in anactive-matrix display.

As for an active-matrix flat panel display (FPD), a liquid crystaldisplay (LCD), an organic electroluminescence (EL) display (OLED), andelectronic paper have been recently realized.

These FPDs are typically driven by a driving circuit containing a TFT,in which amorphous silicon or polycrystalline silicon is used in anactive layer. There are demands for the FPD to be increased in the size,definition, and driving speed thereof. Along with these demands, thereis a need for TFTs, which have high carrier mobility, small agingvariations in the properties, and small variations between the elements.Currently, in addition to silicon, an oxide semiconductor has beenattracted attentions as a semiconductor of the active layer. Among them,InGaZnO₄ (a-IGZO) has characteristics that film formation thereof can becarried out at room temperature, it is amorphous, and it has highmobility of around 10 cm²/V·s. Therefore, developments thereof forpractical use have been actively conducted (see, for example, NPL 1).

The FET typically contains a protective layer for the purpose ofprotecting a semiconductor layer serving as the active layer. Variousresearches have been also conducted on the protective layer.

For example, a SiO₂ layer (see, for example, PTL 1, and PTL 2), a SiNxlayer (see, for example, PTL 1), a SiON layer (see, for example, PTL 3),and an Al₂O₃ layer (see, for example, PTL 4) are disclosed as aprotective layer of the FET. Moreover, a composite oxide layer, in whichSiO₂ forms a composite with Al or B, is disclosed as a protective layerof the FET (see, for example, PTL 5).

When the SiO₂ layer, and the composite oxide layer are formed on thesilicon semiconductor layer, oxide semiconductor layer, metal lines, andoxide lines, there are however a problem that a crack or pealing isformed in a heating process of a post processing. Moreover, the SiONlayer, SiNx layer, and Al₂O₃ layer have a problem that signal delay iscaused due to parasitic capacitance.

Moreover, use of an organic material in the protective layer has beendisclosed.

For example, a polyimide resin layer (see, for example, PTL 6), and afluororesin layer (see, for example, PTL 3) are disclosed as aprotective layer of the FET.

However, a typical organic material has a problem that deterioration ofTFT properties

is caused as the organic material is brought into contact with an oxidesemiconductor. Moreover, the fluororesin layer causes relatively smalldeterioration of the TFT properties, but which is not sufficiently smallfor use.

Accordingly, there is currently a need for a field-effect transistor,which enables high speed operation, and exhibits high reliability.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Application Laid-Open (JP-A) No. 2008-205469-   PTL 2: JP-A No. 2010-103203-   PTL 3: JP-A No. 2007-299913-   PLT 4: JP-A No. 2010-182819-   PLT 5: JP-A No. 2011-77515-   PLT 6: JP-A No. 2011-222788

Non-Patent Literature

-   NPL 1: K. Nomura, and five others, Room-temperature fabrication of    transparent flexible thin-film transistors using amorphous oxide    semiconductors, NATURE, VOL. 432, No. 25, November, 2004, pp.    488-492

SUMMARY OF INVENTION Technical Problem

The present invention aims to solve the aforementioned various problems,and to achieve the following object. Specifically, an object of thepresent invention is to provide a field-effect transistor, which can beoperated at high speed, and has high reliability.

Solution to Problem

The means for solving the aforementioned problems is as follows.

The field-effect transistor of the present invention contains:

a substrate;

a protective layer;

a gate insulating layer formed between the substrate and the protectivelayer;

a source electrode and a drain electrode, which are formed to be incontact with the gate insulating layer;

a semiconductor layer, which is formed at least between the sourceelectrode and the drain electrode, and is in contact with the gateinsulating layer, the source electrode, and the drain electrode; and

a gate electrode, which is formed at an opposite side to the side wherethe semiconductor layer is provided, with the gate insulating layerbeing between the gate electrode and the semiconductor layer, and is incontact with the gate insulating layer,

wherein the protective layer contains a metal oxide composite, whichcontains at least Si and alkaline earth metal.

Advantageous Effects of Invention

The present invention can solve the aforementioned various problems inthe art, and can provide a field-effect transistor, which can beoperated at high speed, and has high reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram for explaining an image display device.

FIG. 2 is a diagram for explaining one example of the display element ofthe present invention.

FIG. 3A is a diagram illustrating one example of the field-effecttransistor of the present invention (bottom contact/bottom gate).

FIG. 3B is a diagram illustrating one example of the field-effecttransistor of the present invention (top contact/bottom gate).

FIG. 3C is a diagram illustrating one example of the field-effecttransistor of the present invention (bottom contact/top gate).

FIG. 3D is a diagram illustrating one example of the field-effecttransistor of the present invention (top contact/top gate).

FIG. 4 is a schematic structure diagram illustrating one example of anorganic EL element.

FIG. 5 is a schematic structure diagram illustrating one example of thedisplay element of the present invention.

FIG. 6 is a schematic structure diagram illustrating another example ofthe display element of the present invention.

FIG. 7 is a diagram for explaining a display control device.

FIG. 8 is a diagram for explaining a liquid crystal display.

FIG. 9 is a diagram for explaining the display element in FIG. 8.

FIG. 10 is a schematic structure diagram of a capacitor for measuringdielectric constant.

FIG. 11 is a graph for evaluating the properties of the field-effecttransistor obtained in Example 1.

FIG. 12 is a graph for evaluating the properties of the field-effecttransistor obtained in Example 1.

FIG. 13 is a graph for evaluating the properties of the field-effecttransistor obtained in Comparative Example 1.

FIG. 14 is a graph for evaluating the properties of the field-effecttransistor obtained in Comparative Example 1.

FIG. 15 is a diagram illustrating the organic EL display device producedin Example 19.

DESCRIPTION OF EMBODIMENTS (Field-Effect Transistor)

The field-effect transistor of the present invention contains at least asubstrate, a protective layer, a gate insulating layer, a sourceelectrode, a drain electrode, a semiconductor layer, and a gateelectrode, and may further contain other members according to thenecessity.

<Substrate>

A shape, structure, and size of the substrate are appropriately selecteddepending on the intended purpose without any limitation.

The material of the substrate is appropriately selected depending on theintended purpose without any limitation, and examples thereof includeglass, and plastic.

The glass is appropriately selected depending on the intended purposewithout any limitation, and examples thereof include non-alkali glass,and silica glass.

The plastic material is appropriately selected depending on the intendedpurpose without any limitation, and examples thereof includepolycarbonate (PC), polyimide (PI), polyethylene terephthalate (PET),and polyethylene naphthalate (PEN).

Note that, a pre-treatment, such as oxygen plasma, UV ozone, and UVradiation washing, is preferably performed on the substrate to clean asurface thereof and to improve adhesion with another layer.

<Protective Layer>

The protective layer is appropriately selected depending on the intendedpurpose without any limitation, provided that the protective layercontains a metal oxide composite containing at least silicon (Si) andalkaline earth metal.

The protective layer is preferably composed of the metal oxide compositeper se.

The protective layer is typically formed at the upper position from thesubstrate.

In the metal oxide composite, SiO₂ composed with Si forms an amorphousstructure. Moreover, the alkaline earth metal has a function of cleavinga Si—O bond. Therefore, dielectric constant and linear expansioncoefficient of the metal oxide composite to be formed can be controlledby a composition ratio.

The metal oxide composite preferably contains Al (aluminum), or B(boron), and a combination of Al and B. Similarly to SiO₂, Al₂O₃composed with Al and B₂O₃ composed with B form an amorphous structure,and therefore an amorphous structure is even more stably obtained in themetal oxide composite, and a more uniform insulating film can be formed.Moreover, the alkaline earth metal also cleaves an Al—O bond and B—Obond, similarly to the Si—O. Therefore, dielectric constant and linearexpansion coefficient of the metal oxide composite to be formed can becontrolled by a composition ratio.

Examples of the alkaline earth metal include Be (beryllium), Mg(magnesium), Ca (calcium), Sr (strontium), and Ba (barium). Among them,preferred are magnesium (Mg), calcium (Ca), strontium (Sr), and barium(Ba).

These alkaline earth metal elements may be used alone or in combination.

A ratio of Si, a ratio of a total of Al and B, and a ratio of thealkaline earth metal in the metal oxide composite are appropriatelyselected depending on the intended purpose without any limitation, butthey are respectively the following ranges.

The ratio of Si in the metal oxide composite based on the oxide (SiO₂)conversion is preferably 30.0 mol % to 95.0 mol %, more preferably 50.0mol % to 90.0 mol %.

The ratio of the alkaline earth metal oxide in the metal oxide compositebased on the oxide (BeO, MgO, CaO, SrO, BaO) conversion is preferably5.0 mol % to 40.0 mol %, more preferably 10.0 mol % to 30.0 mol %.

The ratio of a total of Al and B in the metal oxide composite based onthe oxide (Al₂O₃, B₂O₃) conversion is preferably 1.0 mol % to 50.0 mol%, more preferably 5.0 mol % to 30.0 mol %.

In the case where the metal oxide composite contains Al, or B, or acombination of Al and B, the ratio of the alkaline earth metal oxidebased on the oxide (BeO, MgO, CaO, SrO, BaO) conversion is preferably1.0 mol % to 30.0 mol %, more preferably 5.0 mol % to 20.0 mol %.

The ratio of oxides (SiO₂, BeO, MgO, CaO, SrO, BaO, Al₂O₃, B₂O₃) in themetal oxide composite can be calculated, for example, by analyzing apositive ion element of the oxide by X-ray fluorescence analysis orelectron probe microanalysis (EPMA).

The dielectric constant of the protective layer is appropriatelyselected depending on the intended purpose without any limitation, butit is preferably 7.0 or lower, more preferably 6.0 or lower, as suchdielectric constant of the protective layer can inhibit signal delay,and contribute to high speed operation.

The dielectric constant can be measured, for example, by preparing acapacitor, in which a lower electrode, a dielectric layer (theprotective layer), and an upper electrode are laminated, and measuringby means of LCR meter (4284A, manufactured by Agilent).

The linear expansion coefficient of the protective layer isappropriately selected depending on the intended purpose without anylimitation, but it is preferably 30.0×10⁻⁷ or greater, more preferably30.0×10⁻⁷ to 60.0×10⁻⁷, as with such linear expansion coefficient,pealing is inhibited, and reliability is more enhanced.

The linear expansion coefficient can be measured, for example, by meansof a thermomechanical analysis device (8310 series, manufactured byRigaku Corporation). In this measurement, the linear expansioncoefficient can be measured by measuring a measuring sample, which isseparately produced with the same composition to that of the protectivelayer, without producing the field-effect transistor.

The average thickness of the protective layer is appropriately selecteddepending on the intended purpose without any limitation, but it ispreferably 10 nm to 1,000 nm, and more preferably 20 nm to 500 nm.

—Formation Method of Protective Layer—

A formation method of the protective layer is appropriately selecteddepending on the intended purpose without any limitation, and examplesthereof include a method containing forming a film by a vacuum process,such as sputtering, pulse laser deposition (PLD), chemical vapordeposition (CVD), and atomic layer deposition (ALD), followed bypatterning the film by photolithography.

Moreover, a film can be also formed by preparing a coating liquidcontaining a precursor of the metal oxide composite (a coating liquidfor forming the protective layer), applying or printing the coatingliquid onto a subject to be coated, and baking the applied or printedcoating liquid under the appropriate conditions.

—Coating Liquid for Forming the Protective Layer (Coating Liquid forForming Insulating Film)—

The coating liquid for forming the protective layer (also referred to asa coating liquid for forming an insulating film) contains at least asilicon-containing compound, an alkaline earth metal-containingcompound, and a solvent, preferably further contains analuminum-containing compound, or a boron-containing compound, or theboth, and may further contain other components according to thenecessity.

Currently, developments of printed electronics using a coating process,which can realize low cost production, have been actively conducted, toreplace a vacuum process, which requires expensive equipments, such assputtering, CVD, and dry etching. As for a protective layer of asemiconductor, disclosed are methods for forming a protective layer byapplying polysilazane (see, for example, JP-A No. 2010-103203), orspin-on glass.

However, a coating liquid composed only of SiO₂ precursor, such as ofpolysilazane, and spin-on glass needs to be baked at 450° C. or higherin order to decompose an organic material to form a fine insulatingfilm. In order to decompose an organic material at the temperature equalto or lower than the aforementioned temperature, it is necessary to use,in combination with heating, a reaction accelerating means, such as amicrowave processing (see, for example, JP-A No. 2010-103203), use of acatalyst, and baking in a vapor atmosphere (Japanese Patent (JP-B) No.3666915). Therefore, there are problems, such as a complex bakingprocess, high cost, and reduction in insulating properties due toimpurity residues.

Compared to the above, the coating liquid for forming the protectivelayer contains a precursor of alkaline earth metal oxide, which haslower decomposition temperature than that of the SiO₂ precursor.Therefore, the precursor in the coating liquid for forming theprotective layer is decomposed at temperature lower than that of thecoating liquid composed only of the SiO₂ precursor, i.e., lower than450° C., to form a fine insulating film. As the coating liquid forforming the protective layer further contains an Al₂O₃ precursor, or aB₂O₃ precursor, or a combination thereof, which have, similarly to theprecursor of alkaline earth metal oxide, lower decomposition temperaturethan that of the SiO₂ precursor, an effect of forming a fine insulatingfilm at low temperature can be enhanced.

—Silicon Containing Compound—

Examples of the silicon-containing compound include an inorganic siliconcompound, and an organic silicon compound.

Examples of the inorganic silicon compound include tetrachlorosilane,tetrabromosilane, and tetraiodosilane.

The organic silicon compound is appropriately selected depending on theintended purpose without any limitation, provided that it is a compoundcontaining a silicon atom, and an organic group. The silicon and theorganic group are bonded together, for example, with an ionic bond,covalent bond, or coordinate bond.

The organic group is appropriately selected depending on the intendedpurpose without any limitation, and examples thereof include an alkylgroup that may have a substituent, an alkoxy group that may have asubstituent, an acyloxy group that may have a substituent, and a phenylgroup that may have a substituent. Examples of the alkyl group include aC1-C6 alkyl group. Examples of the alkoxy group include a C1-C6 alkoxygroup. Examples of the acyloxy group include C1-C10 acyloxy group.

Examples of the organic silicon compound include tetramethoxysilane,tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane,1,1,1,3,3,3-hexamethylsilazane (HMDS), bis(trimethylsilyl)acetylene,triphenylsilane, silicon 2-ethylhexanoate, and tetraacetoxysilane.

An amount of the silicon-containing compound in the coating liquid forforming the protective layer is appropriately selected depending on theintended purpose without any limitation.

—Alkaline Earth Metal-Containing Compound—

Examples of the alkaline earth metal-containing compound include aninorganic alkaline earth metal compound, and an organic alkaline earthmetal compound.

Examples of alkaline earth metal in the alkaline earth metal-containingcompound include Be (beryllium), Mg (magnesium), Ca (calcium), Sr(strontium), and Ba (barium).

Examples of the inorganic alkaline earth metal compound include alkalineearth metal nitric acid salt, alkaline earth metal sulfuric acid salt,alkaline earth metal chloride, alkaline earth metal fluoride, alkalineearth metal bromide, alkaline earth metal iodide, and alkaline earthmetal phosphide. Examples of the alkaline earth metal nitric acid saltinclude magnesium nitrate, calcium nitrate, strontium nitrate, andbarium nitrate. Examples of the alkaline earth metal sulfuric acid saltinclude magnesium sulfate, calcium sulfate, strontium sulfate, andbarium sulfate. Examples of the alkaline earth metal chloride includemagnesium chloride, calcium chloride, strontium chloride, and bariumchloride. Examples of the alkaline earth metal fluoride includemagnesium fluoride, calcium fluoride, strontium fluoride, and bariumfluoride. Examples of the alkaline earth metal bromide include magnesiumbromide, calcium bromide, strontium bromide, and barium bromide.Examples of the alkaline earth metal iodide include magnesium iodide,calcium iodide, strontium iodide, and barium iodide. Examples of thealkaline earth metal phosphide include magnesium phosphide, and calciumphosphide.

The organic alkaline earth metal compound is appropriately selecteddepending on the intended purpose without any limitation, provided thatit contains alkaline earth metal and an organic group. The alkalineearth metal and the organic group are bonded together, for example, withan ionic bond, covalent bond, or coordinate bond.

The organic group is appropriately selected depending on the intendedpurpose without any limitation, and examples thereof include an alkylgroup that may have a substituent, an alkoxy group that may have asubstituent, an acyloxy group that may have a substituent, a phenylgroup that may have a substituent, an acetylacetonato group that mayhave a substituent, and a sulfonic acid group that may have asubstituent. Examples of the alkyl group include a C1-C6 alkyl group.Examples of the alkoxy group include a C1-C6 alkoxy group. Examples ofthe acyloxy group include: a C1-C10 acyloxy group; an acyloxy group partof which is substituted with a benzene ring, such as benzoic acid; anacyloxy group part of which is substituted with a hydroxyl group, suchas lactic acid; and an acyloxy group having two or more carbonyl groups,such as oxalic acid, and citric acid.

Examples of the organic alkaline earth metal compound include magnesiummethoxide, magnesium ethoxide, diethyl magnesium, magnesium acetate,magnesium formate, magnesium acetylacetonate, magnesium2-ethylhexanoate, magnesium lactate, magnesium naphthenate, magnesiumcitrate, magnesium salicylate, magnesium benzoate, magnesium oxalate,magnesium trifluoromethanesulfonate, calcium methoxide, calciumethoxide, calcium acetate, calcium formate, calcium acetylacetonate,calcium dipivaloylmethanato, calcium 2-ethylhexanoate, calcium lactate,calcium naphthenate, calcium citrate, calcium salicylate, calciumneodecanoate, calcium benzoate, calcium oxalate, strontium isopropoxide,strontium acetate, strontium formate, strontium acetylacetonate,strontium 2-ethylhexanoate, strontium lactate, strontium naphthenate,strontium salicylate, strontium oxalate, barium ethoxide, bariumisopropoxide, barium acetate, barium formate, barium acetylacetonate,barium 2-ethylhexanoate, barium lactate, barium naphthenate, bariumneodecanoate, barium oxalate, barium benzoate, and bariumtrifluoromethanesulfonate.

An amount of the alkaline earth metal-containing compound in the coatingliquid for forming the protective layer is appropriately selecteddepending on the intended purpose without any limitation.

—Aluminum-Containing Compound—

Examples of the aluminum-containing compound include an inorganicaluminum compound, and an organic aluminum compound.

Examples of the inorganic aluminum compound include aluminum chloride,aluminum nitrate, aluminum bromide, aluminum hydroxide, aluminum borate,aluminum trifluoride, aluminum iodide, aluminum sulfate, aluminumphosphate, and aluminum ammonium sulfate.

The organic aluminum compound is appropriately selected depending on theintended purpose without any limitation, provided that it is a compoundcontaining aluminum and an organic group. The aluminum and the organicgroup are bonded together, for example, with an ionic bond, covalentbond, or coordinate bond.

The organic group is appropriately selected depending on the intendedpurpose without any limitation, and examples thereof include an alkylgroup that may have a substituent, an alkoxy group that may have asubstituent, an acyloxy group that may have a substituent, anacetylacetonato group that may have a substituent, and a sulfonic acidgroup that may have a substituent. Examples of the alkyl group include aC1-C6 alkyl group. Examples of the alkoxy group include a C1-C6 alkoxygroup. Examples of the acyloxy group include: a C1-C10 acyloxy group; anacyloxy group part of which is substituted with a benzene ring, such asbenzoic acid; an acyloxy group part of which is substituted with ahydroxyl group, such as lactic acid; and an acyloxy group having two ormore carbonyl groups, such as oxalic acid, and citric acid.

Examples of the organic aluminum compound include aluminum isopropoxide,aluminum-sec-butoxide, triethyl aluminum, diethyl aluminum ethoxide,aluminum acetate, aluminum acetylacetonate, aluminumhexafluoroacetylacetonate, aluminum 2-ethylhexanoate, aluminum lactate,aluminum benzonate, aluminum di(s-butoxide) acetoacetic ester chelate,and aluminum trifluoromethanesulfonate.

An amount of the aluminum-containing compound in the coating liquid forforming the protective layer is appropriately selected depending on theintended purpose without any limitation.

—Boron-Containing Compound—

Examples of the boron-containing compound include an inorganic boroncompound, and an organic boron compound.

Examples of the inorganic boron compound include orthoboric acid, boronoxide, boron tribromide, tetrafluoroboric acid, ammonium borate, andmagnesium borate. Examples of the boron oxide include diboron dioxide,diboron trioxide, tetraboron trioxide, and tetraboron pentaoxide.

The organic boron compound is appropriately selected depending on theintended purpose without any limitation, provided that it is a compoundcontaining boron and an organic group. The boron and the organic groupare bonded together, for example, with an ionic bond, covalent bond, orcoordinate bond.

The organic group is appropriately selected depending on the intendedpurpose without any limitation, and examples thereof include an alkylgroup that may have a substituent, an alkoxy group that may have asubstituent, an acyloxy group that may have a substituent, a phenylgroup that may have a substituent, a sulfonic acid group that may have asubstituent, and a thiophene group that may have a substituent. Examplesof the alkyl group include a C1-C6 alkyl group. Examples of the alkoxygroup include a C1-C6 alkoxy group. The alkoxy group includes an organicgroup, which contains two or more oxygen atoms among which two oxygenatoms are bonded to boron, and form a ring structure with boron.Moreover, the alkoxy group includes an alkoxy group, where an alkylgroup contained in the alkoxy group is substituted with an organic silylgroup. Examples of the acyloxy group include a C1-C10 acyloxy group.

Examples of the organic boron compound include triethyl borane,(R)-5,5-diphenyl-2-methyl-3,4-propano-1,3,2-oxazaborolidine,triisopropyl borate,2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane,bis(hexyleneglycolato)diboron,4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole,tert-butyl-N-[4-(4,4,5,5-tetramethyl-1,2,3-dioxaborolan-2-yl)phenyl]carbamate,phenyl boronic acid, 3-acetylphenyl boronic acid, boron trifluorideacetic acid complex, boron trifluoride sulfolane complex, 2-thiopheneboronic acid, and tris(trimethylsilyl) borate.

An amount of the boron-containing compound in the coating liquid forforming the protective layer is appropriately selected depending on theintended purpose without any limitation.

—Solvent—

The solvent is appropriately selected depending on the intended purposewithout any limitation, provided that it is a solvent that stablydissolves or disperses the aforementioned various compounds. Examples ofthe solvent include toluene, xylene, mesitylene, isopropanol, ethylbenzoate, N,N-dimethylformamide, propylene carbonate, 2-ethylhexanoate,mineral spirits, dimethylpropylene urea, 4-butyrolactone,2-methoxyethanol, and water.

An amount of the solvent in the coating liquid for forming theprotective layer is appropriately selected depending on the intendedpurpose without any limitation.

A ratio of the silicon-containing compound and the alkaline earthmetal-containing compound (the silicon-containing compound: the alkalineearth metal-containing compound) in the coating liquid for forming theprotective layer is appropriately selected depending on the intendedpurpose without any limitation, but the ratio based on the oxide (SiO₂,BeO, MgO, CaO, SrO, BaO) conversion is preferably 30.0 mol % to 95.0 mol%: 5.0 mol % to 40.0 mol %, more preferably 50.0 mol % to 90.0 mol %:10.0 mol % to 30.0 mol %.

A ratio between the silicon-containing compound, the alkaline earthmetal-containing compound, and a total of the aluminum-containingcompound and the boron-containing compound (the silicon-containingcompound: the alkaline earth metal-containing compound: the total of thealuminum-containing compound and the boron-containing compound) in thecoating liquid for forming the protective layer is appropriatelyselected depending on the intended purpose without any limitation, butthe ratio based on the oxide (SiO₂, BeO, MgO, CaO, SrO, BaO, Al₂O₃,B₂O₃) conversion is preferably 30.0 mol % to 95.0 mol %: 1.0 mol % to30.0 mol %: 1.0 mol % to 50.0 mol %, more preferably 50.0 mol % to 90.0mol %:5.0 mol % to 20.0 mol %: 5.0 mol % to 30.0 mol %.

Formation Method of Protective Layer Using Coating Liquid for Formingthe Protective Layer—

One example of a formation method of the protective layer using thecoating liquid for forming the protective layer is explainedhereinafter.

The formation method of the protective layer contains a coating step,and a heat processing step, and may further contain other stepsaccording to the necessity.

The coating step is appropriately selected depending on the intendedpurpose without any limitation, provided that it contains coating asubject to be coated with the coating liquid for forming the protectivelayer.

A method of the coating is appropriately selected depending on theintended purpose without any limitation, and examples thereof include: amethod containing forming a film through a solution process, followed bypatterning through photolithography; and a method containing directlyforming a film of an intended shape through a printing process, such asinkjet printing, nano printing, and gravure printing.

Examples of the solution process include dip coating, spin coating, diecoating, and nozzle printing.

The heat processing step is appropriately selected depending on theintended purpose without any limitation, provided that subjecting thecoating liquid for forming the protective layer coated on the subject toa heat processing.

Note that, in the heat processing, the coating liquid for forming theprotective layer coated on the subject may be dried by air drying.

The heat processing performs drying of the solvent, generation of themetal oxide composite, etc.

In the heat processing step, the drying of the solvent (referred to as a“drying step” hereinafter), and the generation of the metal oxidecomposite (referred to as a “generation step” hereinafter) arepreferably performed at different temperature.

Specifically, it is preferred that, after drying the solvent, thetemperature be elevated to perform the generation of the metal oxidecomposite.

At the time of the generation of the metal oxide composite, for example,decompositions of the silicon-containing compound, the alkaline earthmetal-containing compound, the aluminum-containing compound, and theboron-containing compound are carried out.

The temperature for the drying step is appropriately selected dependingon a solvent as contained, without any limitation. For example, thetemperature thereof is 80° C. to 180° C. In the drying, it is effectiveto use a vacuum oven to reduce the temperature for the drying.

The duration of the drying step is appropriately selected depending onthe intended purpose without any limitation, and it is, for example, 10minutes to 1 hour.

The temperature of the generation step is appropriately selecteddepending on the intended purpose without any limitation, but it ispreferably 100° C. or higher but lower than 450° C., more preferably200° C. to 400° C.

The duration of the generation step is appropriately selected dependingon the intended purpose without any limitation, and it is, for example,1 hour to 5 hours.

Note that, in the heat processing step, the drying and the generationmay be performed consecutively, or may be performed separately with aplurality of steps.

A method of the heat processing is appropriately selected depending onthe intended purpose without any limitation, and examples thereofinclude a method containing heating the subject to be coated.

The atmosphere of the heat processing is appropriately selecteddepending on the intended purpose without any limitation, but it ispreferably oxygen atmosphere. By performing the heat processing in theoxygen atmosphere, a decomposition product can be promptly dischargedfrom the system, and generation of the metal oxide composite can beaccelerated.

It is effective in the heat processing to apply ultraviolet rays havingthe wavelength of 400 nm or shorter to the material after the drying foraccelerating a reaction of the generation. As ultraviolet rays havingthe wavelength of 400 nm or shorter is applied, chemical bonds of theorganic material contained in the material after the drying are cut, todecompose the organic material. Therefore, the metal oxide composite canbe efficiently formed.

The ultraviolet rays having the wavelength of 400 nm or shorter are isappropriately selected depending on the intended purpose without anylimitation, and examples thereof include ultraviolet rays having thewavelength of 222 nm emitted from an excimer lamp.

Moreover, it is preferred that ozone be applied instead of or inaddition to the application of the ultraviolet rays. By applying theozone to the material after the drying, generation of oxide isaccelerated.

<Gate Insulating Layer>

The gate insulating layer is appropriately selected depending on theintended purpose without any limitation, provided that it is aninsulating layer formed between the substrate and the protective layer.

A material of the gate insulating layer is appropriately selecteddepending on the intended purpose without any limitation, and examplesthereof include: materials that have been widely used formass-production, such as SiO₂, SiN_(x), and Al₂O₃; high dielectricconstant materials, such as La₂O₃, and HfO₂; and organic materials suchas polyimide (PI) and a fluororesin.

—Formation Method of Gate Insulating Layer—

A formation method of the gate insulating layer is appropriatelyselected depending on the intended purpose without any limitation, andexamples thereof include: a vacuum film forming method, such assputtering, chemical vapor deposition (CVD), and atomic layer deposition(ALD); and a printing method, such as spin coating, die coating, andinkjet printing.

The average film thickness of the gate insulating layer is appropriatelyselected depending on the intended purpose without any limitation, butit is preferably 50 nm to 3 μm, more preferably 100 nm to 1 μm.

<Source Electrode and Drain Electrode>

The source electrode and the drain electrode are appropriately selecteddepending on the intended purpose without any limitation, provided thatthey are electrodes for extracting electric current.

The source electrode and the drain electrode are formed to be in contactwith the gate insulating layer.

A material of the source electrode and drain electrode is appropriatelyselected depending on the intended purpose without any limitation, andexamples thereof include: metal, such as Mo, Al, Ag, and Cu; alloythereof; transparent electroconductive oxide, such as indium tin oxide(ITO), and antimony-doped tin oxide (ATO); and organic electroconductor,such as polyethylene dioxythiophene (PEDOT), and polyaniline (PANI).

—Formation Method of Source Electrode and Drain Electrode—

A formation method of the source electrode and the drain electrode isappropriately selected depending on the intended purpose without anylimitation, and examples thereof include: (i) a method containingforming a film through sputtering or dip coating, followed by patterningthe film through photolithography; and (ii) a method containing directlyforming a film of the desired shape through a printing process, such asinkjet printing, nano printing, and gravure printing.

The average film thickness of each of the source electrode and the drainelectrode is appropriately selected depending on the intended purposewithout any limitation, but it is preferably 20 nm to 1 μm, morepreferably 50 nm to 300 nm.

<Semiconductor Layer>

The semiconductor layer is formed at least between the source electrodeand the drain electrode.

The semiconductor layer is in contact with the gate insulating layer,the source electrode, and the drain electrode.

The position “between the source electrode and the drain electrode” isappropriately selected depending on the intended purpose without anylimitation, provided that it is a position where the semiconductor layercan make the field-effect transistor function together with the sourceelectrode and the drain electrode.

A material of the semiconductor layer is appropriately selecteddepending on the intended purpose without any limitation, and examplesthereof include silicon semiconductor, and oxide semiconductor. Examplesof the silicon semiconductor include polycrystalline silicon (p-Si), andamorphous silicon (a-Si). Examples of the oxide semiconductor includeIn—Ga—Zn—O, I—Z—O, and In—Mg—O. Among them, the oxide semiconductor ispreferable.

—Formation Method of Semiconductor Layer—

A formation method of the semiconductor layer is appropriately selecteddepending on the intended purpose without any limitation, and examplesthereof include: a method containing forming a film through a vacuumprocess, such as sputtering, pulse laser deposition (PLD), CVD, andatomic layer deposition (ALD), or a solution process, such as dipcoating, spin coating, and die coating, followed by patterning throughlithography; and a method containing directly forming a film of anintended shape through a printing process, such as inkjet printing, nanoprinting, and gravure printing.

The average film thickness of the semiconductor layer is appropriatelyselected depending on the intended purpose without any limitation, butit is preferably 5 nm to 1 μm, 10 nm to 0.5 μm.

<Gate Electrode>

The gate electrode is formed at an opposite side to the side where thesemiconductor layer is provided, with the gate insulating layer beingbetween the gate electrode and the semiconductor layer.

The gate electrode is in contact with the gate insulating layer.

A material of the gate electrode is appropriately selected depending onthe intended purpose without any limitation, and examples thereofinclude: metal, such as Mo, Al, Ag, and Cu; alloy thereof; transparentelectroconductive oxide, such as indium tin oxide (ITO), andantimony-doped tin oxide (ATO); and organic electroconductor, such aspolyethylene dioxythiophene (PEDOT), and polyaniline (PANI).

—Formation Method of Gate Electrode—

A formation method of the gate electrode is appropriately selecteddepending on the intended purpose without any limitation, and examplesthereof include: (i) a method containing forming a film throughsputtering or dip coating, followed by patterning the film throughphotolithography; and (ii) a method containing directly forming a filmof the desired shape through a printing process, such as inkjetprinting, nano printing, and gravure printing.

The average film thickness of the gate electrode is appropriatelyselected depending on the intended purpose without any limitation, butit is preferably 20 nm to 1 μm, more preferably 50 nm to 300 nm.

A structure of the field-effect transistor is appropriately selecteddepending on the intended purpose without any limitation, and examplesthereof include the following structures of the field-effecttransistors.

(1) A field-effect transistor containing the substrate, the gateelectrode formed on the substrate, the gate insulating layer formed onthe gate electrode, the source electrode and drain electrode both formedon the gate insulating layer, the semiconductor layer formed between thesource electrode and the drain electrode, and the protective layerformed on the semiconductor layer.

(2) A field-effect transistor containing the substrate, the sourceelectrode and drain electrode both formed on the substrate, thesemiconductor layer formed between source electrode and the drainelectrode, the gate insulating layer formed on the source electrode, thedrain electrode, and the semiconductor layer, the gate electrode formedon the gate insulating layer, and the protective layer formed on thegate electrode.

Examples of the field-effect transistor having the structure of (1)include a bottom contact/bottom gate field-effect transistor (FIG. 3A),and a top contact/bottom gate field-effect transistor (FIG. 3B).

Examples of the field-effect transistor having the structure of (2)include a bottom contact/top gate field-effect transistor (FIG. 3C), anda top contact/top gate field-effect transistor (FIG. 3D).

In FIGS. A to 3D, the reference 21 denotes a substrate, 22 denotes agate electrode, 23 denotes a gate insulating layer, 24 denotes a sourceelectrode, 25 denotes a drain electrode, 26 denotes an oxidesemiconductor layer, and 27 denotes a protective layer.

The field-effect transistor can be suitably used for the below-mentioneddisplay element, but use thereof is not limited to the display element.For example, the field-effect transistor can be used for an IC card, IDtag, etc.

(Display Element)

The display element of the present invention contains at least anoptical control element, and a driving circuit configured to drive theoptical control element, and may further contain other members, ifnecessary.

<Optical Control Element>

The optical control element is appropriately selected depending on theintended purpose without any limitation, provided that it is an elementwhich controls optical output according to a driving signal. Examplesthereof include an electroluminescent (EL) element, an electrochromic(EC) element, a liquid crystal element, an electrophoretic element, andan electrowetting element.

<Driving Circuit>

The driving circuit is appropriately selected depending on the intendedpurpose without any limitation, provided that it us a circuit that hasthe field-effect transistor of the present invention, and drives theoptical control element.

<Other Members>

Other members are appropriately selected depending on the intendedpurpose without any limitation.

The display element can achieve a long service optical control and highspeed operation, as the display element contains the field-effecttransistor of the present invention.

(Image Display Device)

The image display device of the present invention contains at least aplurality of display elements, a plurality of lines, and a displaycontrol device, and may further contain other members according to thenecessity.

The image display device is a device configured to display an imageaccording to image data.

<Display Elements>

The display elements are appropriately selected depending on theintended purpose without any limitation, provided that they are thedisplay elements of the present invention arranged in a matrix form.

<Lines>

The lines are appropriately selected depending on the intended purposewithout any limitation, provided that they are each a line configured toindividually apply gate voltage to each field-effect transistor in thedisplay element.

<Display Control Device>

The display control device is appropriately selected depending on theintended purpose without any limitation, provided that it is capable ofindividually controlling the gate voltage of each of the field-effecttransistors through a plurality of the line, according to the imagedata.

<Other Members>

Other members are appropriately selected depending on the intendedpurpose without any limitation.

The image display device can achieve long service life and high speedoperation, as the image display device contains the display element ofthe present invention.

The image display device can be used as a display unit in mobileinformation devices (e.g., a mobile phone, a mobile music player, amobile video player, an electronic book, and personal digital assistant(PDA)) or in imaging devices (e.g., a still camera, and a video camera).Moreover, the image display device can be used as a display unit forvarious information in a transporting system, such as a car, air craft,train, and ship. Further, the image display device can be used as adisplay unit for displaying various information in a measuring device,analysis device, medical device, or advertising media.

(System)

The system of the present invention contains at least the image displaydevice of the present invention, and an image data forming device.

The image data forming device is a device, which is configured to createimage data based on image information to be displayed, and to output theimage data to the image display device.

The display element, image display device, and system of the presentinvention are explained with reference to drawings hereinafter.

First, as one example of the system of the present invention, atelevision device is explained.

The television device, which is one example of the system of the presentinvention, can have a structure, for example, as described in theparagraphs [0038] to [0058] and FIG. 1 of JP-A No. 2010-074148.

Next, the image display device of the present invention is explained.

The image display device of the present invention may have a structure,for example, as described in the paragraphs [0059] to [0060], and FIGS.2 and 3 of JP-A No. 2010-074148.

Next, the display element of the present invention is explained withreference to drawings.

FIG. 1 is a diagram illustrating a display 310 in which display elementsare arranged on a matrix. As illustrated in FIG. 1, the display 310contains “n” number of scanning lines (X0, X1, X2, X3, . . . Xn−2, Xn−1)arranged along the X axis direction with a constant interval, “m” numberof data lines (Y0, Y1, Y2, Y3, . . . Ym−1) arranged along the Y axisdirection with a constant interval, and “m” number of electric currentsupply lines (Y0 i, Y1 i, Y2 i, Y3 i, . . . Ym−1i) arranged along the Yaxis direction with a constant interval.

As described, the display element is specified with the scanning lineand the data line.

FIG. 2 is a schematic structure diagram illustrating one example of thedisplay element of the present invention.

As illustrated in FIG. 2 as an example, the display element contains anorganic EL (luminescent) element 350, and a driving circuit 320 formaking the organic EL element 350 emit. Namely, the display 310 is socalled an active-matrix organic EL display. Moreover, the display 310 isa 32-inch color display. Note that, the size of the display is notlimited to the aforementioned size.

The driving circuit 320 of FIG. 2 will be explained.

The driving circuit 320 contains two field-effect transistors 11 and 12,and a capacitor 13.

The field-effect transistor 11 functions as a switching element. Thegate electrode G is connected with a certain scanning line, and thesource electrode S is connected with a certain data line. Moreover, thedrain electrode D is connected with one terminal of the capacitor 13.

The capacitor 13 is used to store the state of the field-effecttransistor 11, i.e. to store data. The other terminal of the capacitor13 is connected to a certain electric current supply line.

The field-effect transistor 12 is used to supply large electric currentto the organic EL element 350. the gate electrode G is connected to thefield-effect transistor 11 of the drain electrode D. The drain electrodeD is connected to a positive electrode of the organic EL element 350,and the source electrode S is connected to certain electric currentsupply line.

When the field-effect transistor 11 is turned in the “on” state, theorganic EL element 350 is driven by the field-effect transistor 12.

As illustrated in FIG. 3A as one example thereof, the field-effecttransistors 11, 12 each contain a substrate 21, a gate electrode 22, agate insulating layer 23, a source electrode 24, a drain electrode 25,an oxide semiconductor layer 26, and a protective layer 27.

The field-effect transistors 11, 12 can be formed with the materials, bythe process, which are explained in the descriptions of the field-effecttransistor of the present invention.

FIG. 4 is a schematic structure diagram illustrating one example of anorganic EL element.

In FIG. 4, the organic EL element 350 contains a negative electrode 312,a positive electrode 314, and an organic EL thin film layer 340.

A material of the negative electrode 312 is appropriately selecteddepending on the intended purpose without any limitation, and examplesthereof include aluminum (Al), magnesium (Mg)-silver (Ag) alloy,aluminum (A1)-lithium (Li) alloy, and indium tin oxide (ITO). Note that,the magnesium (Mg)-silver (Ag) alloy forms a high reflectance electrodewith a sufficient thickness thereof, and an extremely thin film (lessthan about 20 nm) thereof forms a semi-transparent electrode. In FIG. 4,light is taken out from the side of the positive electrode, but lightcan be taken out from the side of the negative electrode, by making thenegative electrode a transparent or semi-transparent electrode.

A material of the positive electrode 314 is appropriately selecteddepending on the intended purpose without any limitation, and examplesthereof include indium tin oxide (ITO), indium zinc oxide (IZO), andsilver (Ag)-neodymium (Nd) alloy. Note that, in the case where thesilver alloy is used, a resulting electrode becomes a high reflectanceelectrode, which is suitable for taking light out from the side of thenegative electrode.

The organic EL thin film layer 340 contains an electron transportinglayer 342, a light emitting layer 344, and a hole transporting layer346. The electron transporting layer 342 is connected to the negativeelectrode 312, and the hole transporting layer 346 is connected to thepositive electrode 314. The light emitting layer 344 emits light, as thepredetermined voltage is applied between the positive electrode 314 andthe negative electrode 312.

Here, the electron transporting layer 342 and the light emitting layer344 may form one layer. Moreover, an electron injecting layer may beprovided between the electron transporting layer 342 and the negativeelectrode 312. Further, a hole injecting layer may be provided betweenthe hole transporting layer 346 and the positive electrode 314.

In FIG. 4, as for the optical control element, the so-called “bottomemission” organic EL element, in which light is taken out from the sideof the substrate, is explained. However, the optical control element maybe a “top emission” organic EL element, in which light is taken out fromthe opposite side to the substrate.

FIG. 5 depicts one example of the display element, in which the organicEL element 350 and the driving circuit 320 are combined.

The display element contains a substrate 31, first and second gateelectrodes 32, 33, a gate insulating layer 34, first and second sourceelectrodes 35, 36, first and second drain electrodes 37, 38, first andsecond oxide semiconductor layers 39, 40, first and second protectivelayers 41, 42, an interlayer insulating film 43, an organic EL layer 44,and a negative electrode 45. The first drain electrode 37 and the secondgate electrode 33 are connected to the gate insulating layer 34 via athrough-hole.

It is appeared in FIG. 5 that a capacitor is formed between the secondgate electrode 33 and the second drain electrode 38 as a matter ofpractical convenience. In fact, a position at which a capacitor isformed is not restricted, and a capacitor having an appropriate capacitycan be provided in an appropriate position.

In the display element of FIG. 5, moreover, the second drain electrode38 functions as a positive electrode of the organic EL element 350.

The substrate 31, first and second gate electrodes 32, 33, gateinsulating layer 34, first and second source electrodes 35, 36, firstand second drain electrodes 37, 38, first and second oxide semiconductorlayers 39, 40, and first and second protective layers 41, 42 can beformed with the materials, by the process explained in the descriptionsof the field-effect transistor of the present invention.

A material of the interlayer insulating film 43 (leveling film) isappropriately selected depending on the intended purpose without anylimitation, and examples thereof include: a resin, such as polyimide,acryl, and a fluororesin; a photosensitive resin using any of theaforementioned resins, and SOG (spin on glass). A process for formingthe interlayer insulating film is appropriately selected depending onthe intended purpose without any limitation. For example, a film may bedirectly formed to have a desired shape by spin coating, inkjetprinting, slit coating, nozzle printing, gravure printing, or dipcoating. In case of a photosensitive material, the film may be patternedby photolithography.

Production methods of the organic EL layer 44 and the negative electrode45 are appropriately selected depending on the intended purpose withoutany limitation, and examples thereof include: a vacuum film formingmethod, such as vacuum deposition and sputtering; and a solutionprocess, such as inkjet printing, and nozzle coating.

In the manner as described above, the display element that is theso-called “bottom emission” organic EL element, in which light is guidedout from the side of the substrate, can be produced. In this case, thesubstrate 31, gate insulating layer 34, and second drain electrode(positive electrode) 38 need to be transparent.

In FIG. 5, a structure where the organic EL element 350 is provided nextto the driving circuit 320. However, the display element may have astructure where the organic EL element 350 is provided above the drivingcircuit 320 as illustrated in FIG. 6. In this case, the organic ELelement is also “bottom emission” type where emission light is guidedout from the side of the substrate, and therefore the driving circuit320 needs to be transparent. As for the source and drain electrodes orpositive electrode, use of transparent electroconductive oxide, such asITO, In₂O₃, SnO₂, ZnO, Ga-doped ZnO, Al-doped ZnO, and Sb-doped SnO₂, ispreferable.

The display control device 400 contains an image data processing circuit402, a scanning line driving circuit 404, and a data line drivingcircuit 406, as illustrated in FIG. 7 as an example.

The image data processing circuit 402 judges brightness of a pluralityof display elements 302 in a display 310, based on an output signal ofan image output circuit.

The scanning line driving circuit 404 individually applies voltage tothe number “n” of scanning lines according to the instruction of theimage data processing circuit 402.

The data line driving circuit 406 individually applies voltage to thenumber “m” of data lines according to the instruction of the image dataprocessing circuit 402.

Note that, in the present embodiment, a case where the organic EL thinfilm layer is composed of the electron transporting layer, the lightemitting layer, and the hole transporting layer, is explained, but notlimited thereto. For example, the electron transporting layer and thelight emitting layer may form one layer. Moreover, an electron injectinglayer may be provided between the electron transporting layer and thenegative electrode. Further, a hole injecting layer may be providedbetween the hole transporting layer and the positive electrode.

Moreover, the case of “bottom emission” where emission light is guidedout from the side of the substrate is explained in the presentembodiment, but not limited thereto. For example, light may be guidedout from the opposite side of the substrate by using a high reflectanceelectrode, such as silver (Ag)-neodymium (Nd) alloy, as the positiveelectrode 314, and using a semi-transparent electrode (e.g., magnesium(Mg)-silver (Ag) alloy or a transparent electrode (e.g. ITO), as thenegative electrode 312.

Moreover, a case where the optical control element is the organic ELelement is explained in the present embodiment, but not limited thereto.For example, the optical control element may be an electrochromicelement. In this case, the display 310 becomes an electrochromicdisplay.

Moreover, the optical control element may be a liquid crystal element.In this case, the display 310 becomes a liquid crystal. As illustratedin FIG. 8 as an example, it is not necessary to provide an electriccurrent supply line for the display element 302′.

In this case, moreover, the driving circuit 320′ can be composed of onefield-effect transistor 14 that is similar to the aforementionedfield-effect transistor (11, 12), and a capacitor 15, as illustrated inFIG. 9 as an example. In the field-effect transistor 14, the gateelectrode G is connected to a certain scanning line, and the sourceelectrode S is connected to a certain data line. Moreover, the drainelectrode D is connected to a pixel electrode of the liquid crystalelement 370, and to the capacitor 15. Note that, the references in FIG.9, 16, 372 are each a counter electrode (common electrode) of the liquidcrystal element 370.

In the present embodiment, the optical control element may be anelectrophoretic element. Alternatively, the optical control element maybe an electrowetting element.

Moreover, in the present embodiment, the case where the display is colordisplay is explained, but not limited to such case.

Note that, the field-effect transistor according to the presentembodiment can be used products (e.g., an IC card, and an ID tag) otherthan the display element.

Since the field-effect transistor of the present invention has highoperation speed and high reliability, the same effects can be attainedwith the display element, image display device, and system, each usingthe field-effect transistor.

EXAMPLES

Examples of the present invention will be explained hereinafter, butExamples shall not be construed as to limit the scope of the presentinvention. In Examples below, “%” represents “% by mass” unlessotherwise stated.

Examples 1 to 4 <Production of Field-Effect Transistor> —Preparation ofCoating Liquid for Forming Protective Layer—

According to the amounts depicted in Table 1, tetrabutoxy silane(T5702-100G, of Aldrich), aluminum di(s-butoxide)acetoacetic acid esterchelate (Al content: 8.4%, Alfa 89349, of Alfa Aesar), triisopropylborate (Wako 320-41532, manufactured by Wako Chemical Ltd.), a calcium2-ethylhexanoate mineral sprits solution (Ca content: 5%, Wako351-01162, manufactured by Wako Chemical Ltd.), and a strontium2-ethylhexanoate toluene solution (Sr content: 2%, Wako 195-09561,manufactured by Wako Pure Chemical Industries, Ltd.) were diluted withtoluene, to thereby obtain a coating liquid for forming a protectivelayer. The metal oxide formed by the coating liquid for forming theprotective layer had the composition as depicted in Table 2.

Next, a bottom contact/bottom gate field-effect transistor, asillustrated in FIG. 3A, was produced.

—Formation of Gate Electrode—

First, a gate electrode 22 was formed on a glass substrate (substrate21). Specifically, a Mo (molybdenum) film was formed on the glasssubstrate (substrate 21) by DC sputtering so that the average filmthickness of the Mo (molybdenum) film was to be about 100 nm.Thereafter, a photoresist was applied on the Mo film, and thephotoresist was then subjected to pre-baking, light exposure by anexposure device, and developing, to thereby form a resist pattern, whichwas identical to a pattern of the gate electrode 22 to be formed. Then,the region of the Mo film, on which the resist pattern had not beenformed, was removed by reactive ion etching (RIE). Thereafter, theremained resist pattern was removed, to thereby form the gate electrode22 formed of the Mo film.

—Formation of Gate Insulating Layer—

Next, a gate insulating layer 23 was formed on the gate electrode 22.Specifically, an Al₂O₃ film was formed on the gate electrode 22 and theglass substrate (substrate 21) by RF sputtering so that the average filmthickness of the Al₂O₃ film was to be about 300 nm, to thereby form thegate insulating layer 23.

—Formation of Source Electrode and Drain Electrode—

Next, a source electrode 24 and a drain electrode 25 were formed on thegate insulating layer 23. Specifically, a Mo (molybdenum) film wasformed on the gate insulating layer 23 by DC sputtering so that theaverage film thickness of the Mo film was to be about 100 nm.Thereafter, a photoresist was applied on the Mo film, and thephotoresist was then subjected to pre-baking, light exposure by anexposure device, and developing, to thereby form a resist pattern, whichwas identical to a pattern of the source electrode 24 and drainelectrode 25 to be formed. Then the region of the Mo film, on which theresist pattern had not been formed, was removed. Thereafter, theremaining resist pattern was removed, to thereby form the sourceelectrode 24 and the drain electrode 25, each of which was formed of theMo film.

—Formation of Oxide Semiconductor Layer—

Next, an oxide semiconductor layer 26 was formed. Specifically, a Mg—Inoxide (In₂MgO₄) film was formed by DC sputtering so that the averagefilm thickness was to be about 100 nm. Thereafter, a photoresist wasapplied on the Mg—In oxide film, and the photoresist was then subjectedto pre-baking, light exposure by an exposure device, and developing, tothereby form a resist pattern, which was identical to a pattern of theoxide semiconductor layer 26 to be formed. The region of the Mg—In oxidefilm, on which the resist pattern had not been formed, was removed bywet etching. Thereafter, the resist pattern was removed, to thereby formthe oxide semiconductor layer 26. As a result, the oxide semiconductorlayer 26 was formed so that a channel was formed between the sourceelectrode 24 and the drain electrode 25.

—Formation of Protective Layer—

Next, 0.4 mL of the coating liquid for forming the protective layer wasapplied onto the substrate drop wise, and the applied coating liquid wasspin coated under certain conditions (after rotating at 300 rpm for 5seconds, rotating at 3,000 rpm for 20 second, followed by stopping therotation to 0 rpm for 5 seconds). Subsequently, the applied coatingliquid was dried in the atmosphere at 120° C. for 1 hour, followed bybaking in the 02 atmosphere at 400° C. for 3 hours, to thereby form aSiO2-A₂O₃—B₂O₃—CaO—SrO metal oxide composite insulating film (protectivelayer), as the protective layer 27. In this manner, the field-effecttransistor was completed.

The average film thickness of the protective layer 27 was about 30 nm.

Finally, as for a heat processing of a post treatment, the heatprocessing was performed at 320° C. for 30 minutes, followed bysubjecting the protective layer 27 of the field-effect transistor toevaluation of an appearance. The result is presented in Table 2.

<Production of Capacitor for Measuring Dielectric Constant>

A capacitor having the structure illustrated in FIG. 10 was produced.First, a lower electrode 82 was formed on a glass substrate 81.Specifically, a Mo (molybdenum) film was formed through a metal mask byDC sputtering so that the average film thickness thereof was to be about100 nm. Next, a dielectric layer 83 was formed in the same process tothat of the formation of the protective layer of the field-effecttransistor of each Example. Finally, an upper electrode 84 was formed onthe dielectric layer 83 with the same material and in the same processto those of the lower electrode 82, to thereby produce the capacitor.The average film thickness of the dielectric layer 83 was 30 nm. Thedielectric constant of the produced capacitor was measured by means of aLCR meter (4284A, of Agilent). The results are presented in Table 2.

<Production of Sample for Measuring Linear Expansion Coefficient>

The coating liquid for forming the protective layer (1 L) of eachExample was prepared, followed by removing the solvent. The resultantwas placed in a platinum crucible, and was heated and melted at 1,600°C., followed by producing a cylindrical object having a diameter of 5 mmand height of 10 mm by a float process. The produced cylindrical objectwas subjected to the measurement of the average liner expansioncoefficient in the temperature range of 20° C. to 300° C. by means of athermomechanical analysis device (8310 series, manufactured by RigakuCorporation). The produced cylindrical object had the same compositionto that of the protective layer of the field-effect transistor of eachExample, and therefore would have the same linear expansion coefficientto that of the protective layer of the field-effect transistor of eachExample.

TABLE 1 Mass/g Ex. 1 Ex. 2 Ex. 3 Ex. 4 tetrabutoxy silane 1.68 1.74 1.501.75 aluminum di(s-butoxide)acetoacetic acid 0.52 0.57 0.42 0.69 esterchelate triisopropyl borate 0.34 0.36 0.32 0.39 calcium 2-ethylhexanoatemineral spirits 0.45 0.23 0.28 0.05 solution (Ca content: 5%) strontium2-ethylhexanoate toluene 0.86 0.66 5.04 0.40 solution (Sr content: 2%)toluene 5.37 5.78 1.44 6.33

TABLE 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Oxide Oxide Oxide Oxide Oxide OxideOxide Oxide mass molar mass molar mass molar mass molar ratio ratioratio ratio ratio ratio ratio ratio Oxide mass % mol % mass % mol % mass% mol % mass % mol % SiO₂ 61.0 67.5 62.8 70.0 50.9 60.3 62.3 70.3 Al₂O₃16.4 10.7 18.1 11.9 12.3 8.6 21.5 14.3 B₂O₃ 12.3 11.8 12.8 12.3 10.811.1 13.7 13.4 MgO — — — — — — — — CaO 6.2 7.4 3.2 3.8 3.7 4.7 0.7 0.8SrO 4.0 2.6 3.1 2.0 22.3 15.3 1.8 1.2 BaO — — — — — — — — total 100.0100.0 100.0 100.0 100.0 100.0 100.0 100.0 Dielectric 5.5 5.0 6.0 4.8constant Linear 36.4 30.0 50.3 24.7 expansion coefficient (×10⁻⁷/K⁻¹)Appearance No pealing No pealing No pealing No pealing

In Table 2, “-” denotes that the ratio is 0%, which is the same inTables 4, 6, 8, 11, 12, 13, and 15.

Examples 5 to 7

According to the amounts depicted in Table 3, 1,1,1,3,3,3-hexamethyldisilazane (HMDS, manufactured by Tokyo Ohka Kogyo Co., Ltd.), aluminumdi(s-butoxide)acetoacetic acid ester chelate (Al content: 8.4%, Alfa89349, of Alfa Aesar), phenyl borate (Wako 163-23222, manufactured byWako Pure Chemical Industries, Ltd.), a magnesium 2-ethylhexanoatetoluene solution (Mg content: 3%, Stream 12-1260, manufactured by StremChemicals, Inc.), a calcium 2-ethylhexanoate mineral sprits solution (Cacontent: 5%, Wako 351-01162, manufactured by Wako Chemical Ltd.), astrontium 2-ethylhexanoate toluene solution (Sr content: 2%, Wako195-09561, manufactured by Wako Pure Chemical Industries, Ltd.), and abarium 2-ethylhexanoate toluene solution (Ba content: 8%, Wako021-09471, manufactured by Wako Pure Chemical Industries, Ltd.) werediluted with toluene, to thereby obtain a coating liquid for forming aprotective layer. The metal oxide formed by the coating liquid forforming the protective layer had the composition as depicted in Table 4.

A field-effect transistor, a capacitor, and a cylindrical object wereproduced using the prepared coating liquid for forming the protectivelayer in the same manners as in Example 1, and were evaluated in thesame manners as in Example 1. The results are presented in Table 4.

TABLE 3 Mass/g Ex. 5 Ex. 6 Ex. 7 HMDS 0.41 0.41 0.41 aluminumdi(s-butoxide)acetoacetic acid ester 0.52 0.52 0.52 chelate phenylborate 0.23 0.23 0.23 magnesium 2-ethylhexanoate toluene solution 0.45 —— (Mg content: 3%) calcium 2-ethylhexanoate mineral spirits 0.16 — —solution (Ca content: 5%) strontium 2-ethylhexanoate toluene solution —2.44 3.29 (Sr content: 2%) barium 2-ethylhexanoate toluene solution (Ba— 0.34 — content: 8%) toluene 4.91 2.92 3.15

TABLE 4 Ex. 5 Ex. 6 Ex. 7 Oxide Oxide Oxide Oxide Oxide Oxide mass molarmass molar mass molar ratio ratio ratio ratio ratio ratio Oxide mass %mol % mass % mol % mass % mol % SiO₂ 63.3 67.5 56.9 67.5 57.9 67.5 Al₂O₃17.0 10.7 15.3 10.7 15.6 10.7 B₂O₃ 12.8 11.8 11.5 11.8 11.7 11.8 MgO 4.67.4 — — — — CaO 2.3 2.6 — — — — SrO — — 10.7 7.4 14.8 10.0 BaO — — 5.62.6 — — Total 100.0 100.0 100.0 100.0 100.0 100.0 Dielectric 5.0 5.8 6.0constant Linear 30.8 39.5 38.6 expansion coefficient (×10⁻⁷/K⁻¹)Appearance No pealing No pealing No pealing

Examples 8 and 9

According to the amounts depicted in Table 5, 1,1,1,3,3,3-hexamethyldisilazane (HMDS, manufactured by Tokyo Ohka Kogyo Co., Ltd.), aluminumdi(s-butoxide)acetoacetic acid ester chelate (Al content: 8.4%, Alfa89349, of Alfa Aesar), a magnesium 2-ethylhexanoate toluene solution (Mgcontent: 3%, Stream 12-1260, manufactured by Strem Chemicals, Inc.), anda strontium 2-ethylhexanoate toluene solution (Sr content: 2%, Wako195-09561, manufactured by Wako Pure Chemical Industries, Ltd.) werediluted with toluene, to thereby prepare a coating liquid for forming aprotective layer. The metal oxide formed by the coating liquid forforming the protective layer had the composition as depicted in Table 6.

A field-effect transistor, a capacitor, and a cylindrical object wereproduced using the prepared coating liquid for forming the protectivelayer in the same manners as in Example 1, and were evaluated in thesame manners as in Example 1. The results are presented in Table 6.

TABLE 5 Mass/g Ex. 8 Ex. 9 HMDS 0.44 0.44 aluminumdi(s-butoxide)acetoacetic acid ester 0.86 0.86 chelate magnesium2-ethylhexanoate toluene solution 0.26 — (Mg content: 3%) strontium2-ethylhexanoate toluene solution (Sr 1.91 3.29 content: 2%) toluene2.25 0.81

TABLE 6 Ex. 8 Ex. 9 Oxide Oxide Oxide Oxide mass molar mass molar ratioratio ratio ratio Oxide mass % mol % mass % mol % SiO₂ 62.5 72.1 60.272.1 Al₂O₃ 26.3 17.9 25.4 17.9 B₂O₃ — — — — MgO  2.4  4.2 — — CaO — — —— SrO  8.7  5.8 14.4 10.0 BaO — — — — Total 100.0  100.0  100.0  100.0 Dielectric constant 5.9 6.0 Linear expansion 30.2 34.4 coefficient(×1E⁻⁷/K⁻¹) Appearance No pealing No pealing

Examples 10 and 11

According to the amounts depicted in Table 7, 1,1,1,3,3,3-hexamethyldisilazane (HMDS, manufactured by Tokyo Ohka Kogyo Co., Ltd.),2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxadioxaborolane (Wako325-41462, manufactured by Wako Chemical Ltd.), a calcium2-ethylhexanoate mineral spirits solution (Ca content: 5%, Wako351-01162, manufactured by Wako Chemical Ltd.), and a barium2-ethylhexanoate toluene solution (Ba content: 8%, Wako 021-09471,manufactured by Wako Pure Chemical Industries, Ltd.) were diluted withtoluene, to thereby prepare a coating liquid for forming a protectivelayer. The metal oxide formed by the coating liquid for forming theprotective layer had the composition as depicted in Table 8.

A field-effect transistor, a capacitor, and a cylindrical object wereproduced using the prepared coating liquid for forming the protectivelayer in the same manners as in Example 1, and were evaluated in thesame manners as in Example 1. The results are presented in Table 8.

TABLE 7 Mass/g Ex. 10 Ex. 11 HMDS 0.43 0.432-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane 0.57 0.57 calcium2-ethylhexanoate mineral spirits solution (Ca 0.40 — content: 5%) barium2-ethylhexanoate toluene solution (Ba 0.43 1.29 content: 8%) toluene4.23 3.26

TABLE 8 Ex. 10 Ex. 11 Oxide Oxide Oxide Oxide mass molar mass molarratio ratio ratio ratio Oxide mass % mol % mass % mol % SiO₂ 65.7 70.859.7 70.8 Al₂O₃ — — — — B₂O₃ 20.6 19.2 18.8 19.2 MgO — — — — CaO  5.8 6.7 — — SrO — — — — BaO  7.8  3.3 21.5 10.0 Total 100.0  100.0  100.0 100.0  Dielectric 4.7 4.4 constant Linear expansion 33.7 43.0coefficient (×10⁻⁷/K⁻¹) Appearance No pealing No pealing

Examples 12 to 18

According to the amounts depicted in Tables 9 and 10, tetrabutoxy silane(T5702-100G, of Aldrich), a magnesium 2-ethylhexanoate toluene solution(Mg content: 3%, Stream 12-1260, manufactured by Strem Chemicals, Inc.),a calcium 2-ethylhexanoate mineral spirits solution (Ca content: 5%,Wako 351-01162, manufactured by Wako Chemical Ltd.), a strontium2-ethylhexanoate toluene solution (Sr content: 2%, Wako 195-09561,manufactured by Wako Pure Chemical Industries, Ltd.), and a barium2-ethylhexanoate toluene solution (Ba content: 8%, Wako 021-09471,manufactured by Wako Pure Chemical Industries, Ltd.) were diluted withtoluene, to thereby prepare a coating liquid for forming a protectivelayer. The metal oxide formed by the coating liquid for forming theprotective layer had the composition as depicted in Tables 11 and 12.

A field-effect transistor, a capacitor, and a cylindrical object wereproduced using the prepared coating liquid for forming the protectivelayer in the same manners as in Example 1, and were evaluated in thesame manners as in Example 1. The results are presented in Tables 11 and12.

TABLE 9 Mass/g Ex. 12 Ex. 13 Ex. 14 Ex. 15 tetrabutoxy silane 2.24 1.991.74 1.61 Magnesium 2-ethylhexanoate 0.26 0.62 1.05 1.05 toluenesolution (Mg content: 3%) calcium 2-ethylhexanoate mineral — — — —spirits solution (Ca content: 5%) strontium 2-ethylhexanoate toluene1.91 3.23 4.22 5.83 solution (Sr content: 2%) barium 2-ethylhexanoatetoluene — — — — solution (Ba content: 8%) toluene 3.12 1.68 0.52 —

TABLE 10 Mass/g Ex. 16 Ex. 17 Ex. 18 tetrabutoxy silane 1.99 1.99 1.99magnesium 2-ethylhexanoate toluene 0.89 — — solution (Mg content: 3%)calcium 2-ethylhexanoate mineral spirits — 0.70 1.21 solution (Cacontent: 5%) strontium 2-ethylhexanoate toluene solution — 2.77 — (Srcontent: 2%) barium 2-ethylhexanoate toluene solution 0.70 — — (Bacontent: 8%) toluene 3.94 2.06 4.32

TABLE 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Oxide Oxide Oxide Oxide Oxide OxideOxide Oxide mass molar mass molar mass molar mass molar ratio ratioratio ratio ratio ratio ratio ratio Oxide mass % mol % mass % mol % mass% mol % mass % mol % SiO₂ 87.5  90.0  77.1 80.0 67.6 70.0 60.7 65.0Al₂O₃ — — — — — — — — B₂O₃ — — — — — — — — MgO 2.7 4.2  6.6 10.2 11.117.2 10.8 17.3 CaO — — — — — — — — SrO 9.7 5.8 16.3  9.8 21.3 12.8 28.517.7 BaO — — — — — — — — Total 100.0  100.0  100.0  100.0  100.0  100.0 100.0  100.0  Dielectric 4.6  5.2  5.5  6.2 constant Linear 30.2  41.855.3 63.4 expansion coefficient (×10⁻⁷/K⁻¹) Appearance No pealing Nopealing No pealing No pealing

TABLE 12 Ex. 16 Ex. 17 Ex. 18 Oxide Oxide Oxide Oxide Oxide Oxide massmolar mass molar mass molar ratio ratio ratio ratio ratio ratio Oxidemass % mol % mass % mol % mass % mol % SiO₂ 77.2 80.0 76.0 80.0 81.180.0 Al₂O₃ — — — — — — B₂O₃ — — — — — — MgO 9.5 14.6 — — — — CaO — —10.3 11.6 18.9 20.0 SrO — — 13.8 8.4 — — BaO 13.3 5.4 — — — — Total100.0 100.0 100.0  100.0 100.0  100.0  Dielectric 5.4 5.7 5.8 constantLinear 39.6 34.4 46.0 expansion coefficient (×10⁻⁷/K⁻¹) Appearance Nopealing No pealing No pealing

Comparative Example 1 <Production of Field-Effect Transistor>

First, a gate electrode, a gate insulating layer, a source electrode anda drain electrode, and an oxide semiconductor layer were formed on aglass substrate in the same manners as in Example 1.

—Formation of Protective Layer—

Next, a protective layer was formed. Specifically, 0.4 mL of afluororesin coating liquid (Cytop CTL-809A, manufactured by ASAHI GLASSCO., LTD.) was applied by spin coating (rotated at 500 rpm for 10seconds, followed by rotated at 2,000 rpm for 30 seconds). Next, theapplied coating liquid was prebaked at 90° C. for 30 minutes, followedby postbaking at 230° C. for 60 minutes, to thereby form the protectivelayer to cover the oxide semiconductor layer. The protective layerformed in this manner had the average film thickness of about 1,500 nm.

Finally, as for a heat processing of a post treatment, the heatprocessing was performed at 320° C. for 30 minutes, followed bysubjecting the protective layer 27 of the field-effect transistor toevaluation of an appearance. The result is presented in Table 13.

<Production of Capacitor for Measuring Dielectric Constant>

A capacitor having the structure illustrated in FIG. 10 was produced.First, a lower electrode 82 was formed on a glass substrate 81.Specifically, a Mo (molybdenum) film was formed through a metal mask byDC sputtering so that the average film thickness thereof was to be about100 nm. Next, a dielectric layer 83 was formed in the same process tothat of the formation of the protective layer of the field-effecttransistor of Comparative Example 1. Finally, an upper electrode 84 wasformed on the dielectric layer 83 with the same material and in the sameprocess to those of the lower electrode 82, to thereby produce thecapacitor. The average film thickness of the dielectric layer 83 was1,500 nm. The dielectric constant of the produced capacitor was measuredby means of a LCR meter (4284A, of Agilent). The result is presented inTable 13.

<Production of Sample for Measuring Linear Expansion Coefficient>

First, a fluororesin coating liquid (Cytop CTL-809 A, manufactured byASAHI GLASS CO., LTD.) was diluted to 2-fold with a fluorine-basedsolvent (CT-SOLV180, manufactured by ASAHI GLASS CO., LTD.), to therebyprepare a coating liquid. Next, 0.4 mL of the coating liquid was appliedon a monocrystal Si substrate by spin coating (rotated at 500 rpm for 10seconds, followed by rotated at 1,000 rpm for 30 seconds). Subsequently,the applied coating liquid was prebaked at 90° C. for 30 minutes,followed by post baking at 230° C. for 60 minutes, to thereby prepare asample for measuring linear expansion coefficient. The average filmthickness of the sample was 300 nm. The produced sample for measuringlinear expansion coefficient was subjected to the measurement of theaverage linear expansion coefficient in the temperature range of 20° C.to 80° C. by X-ray reflectometry. The result is presented in Table 13.

Comparative Example 2 <Production of Field-Effect Transistor>

First, a gate electrode, a gate insulating layer, a source electrode anda drain electrode, and an oxide semiconductor layer were formed on aglass substrate in the same manner as in Example 1.

—Formation of Protective Layer—

Next, a protective layer was formed. Specifically, a SiO₂ layer wasformed as a protective layer using SiCl₄ as a raw material by plasmaenhanced chemical vapor deposition (PECVD), to complete a field-effecttransistor. The protective layer formed in this manner had the averagefilm thickness of about 30 nm.

Finally, as for a heat processing of a post treatment, the heatprocessing was performed at 320° C. for 30 minutes, followed bysubjecting the protective layer 27 of the field-effect transistor toevaluation of an appearance. The result is presented in Table 13.

<Production of Capacitor for Measuring Dielectric Constant>

A capacitor having the structure illustrated in FIG. 10 was produced.First, a lower electrode 82 was formed on a glass substrate 81.Specifically, a Mo (molybdenum) film was formed through a metal mask byDC sputtering so that the average film thickness thereof was to be about100 nm. Next, a dielectric layer 83 was formed in the same process tothat of the formation of the protective layer of the field-effecttransistor of Comparative Example 2. Finally, an upper electrode 84 wasformed on the dielectric layer 83 with the same material and in the sameprocess to those of the lower electrode 82, to thereby produce thecapacitor. The average film thickness of the dielectric layer 83 was 30nm. The dielectric constant of the produced capacitor was measured bymeans of a LCR meter (4284A, of Agilent). The results are presented inTable 13.

<Production of Sample for Measuring Linear Expansion Coefficient>

SiCl₄ was used as a raw material. The silica powder was grown throughhydrolysis performed in oxygen-hydrogen flame to thereby obtain a SiO₂porous material. The SiO₂ porous material was melted at high temperatureof 1,600° C., to thereby prepare cylindrical SiO₂ glass having adiameter of 5 mm, and height of 10 mm. The produced cylindrical glasswas subjected to the measurement of the average linear expansioncoefficient in the temperature range of 20° C. to 300° C. by means of athermomechanical analysis device (8310 series, manufactured by RigakuCorporation). The produced cylindrical glass had the same composition tothat of the protective layer of the field-effect transistor ofComparative Example 2, and therefore would have the same linearexpansion coefficient to that of the protective layer of thefield-effect transistor of Comparative Example 2.

TABLE 13 Comp. Ex. 2 Oxide Oxide mass molar ratio ratio Oxide Comp. Ex.1 mass % mol % SiO₂ Foluororesin 100 100 Al₂O₃ — — B₂O₃ — — MgO — — CaO— — SrO — — BaO — — Total 100 100 Dielectric 2.1 3.9 constant Linearexpansion 1200.0 5.0 coefficient (×10⁻¹/K⁻¹) Appearance No pealingPealed

Comparative Examples 3 and 4

According to the amounts depicted in Table 14, tetrabutoxy silane(T5702-100 G, of Aldrich), aluminum di(s-butoxide)acetoacetic acid esterchelate (Al content: 8.4%, Alfa 89349, of Alfa Aesar), and2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (Wako 325-41462,manufactured by Wako Chemical Ltd.) were diluted with toluene, tothereby obtain a coating liquid for forming a protective layer. Themetal oxide formed by the coating liquid for forming the protectivelayer had the composition as depicted in Table 15.

A field-effect transistor, a capacitor, and a cylindrical object wereproduced using the prepared coating liquid for forming the protectivelayer in the same manners as in Example 1, and were evaluated in thesame manners as in Example 1. The results are presented in Table 15.

TABLE 14 Mass/g Comp. Comp. Ex. 3 Ex. 4 tetrabutoxy silane 2.08 2.10aluminum di(s-butoxide)acetoacetic acid ester 0.78 — chelate2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane — 0.46 toluene 5.876.14

TABLE 15 Comp. Ex. 3 Comp. Ex. 4 Oxide Oxide Oxide Oxide mass molar massmolar ratio ratio ratio ratio Oxide mass % mol % mass % mol % SiO₂ 75.383.8 82.4 84.4 Al₂O₃ 24.7 16.2 — — B₂O₃ — — 17.6 15.6 MgO — — — — CaO —— — — SrO — — — — BaO — — — — Total 100.0  100.0  100.0  100.0 Dielectric 5.1 3.6 constant Linear expansion 12.9 17.4 coefficient(×10⁻⁷/K⁻¹) Appearance Pealed Pealed

<Appearance of Field-Effect Transistor, and Dielectric Constant andLinear Expansion Coefficient of Protective Layer>

It was confirmed that the protective layers of the field-effecttransistors of Comparative Examples 2 to 4 were pealed in the positionabove the source electrode 24 and the drain electrode 25, each formed ofthe Mo film, or above the oxide semiconductor layer 26 formed of theMg—In oxide (In₂MgO₄) film.

This is probably because stress was caused at the interface between theMo film or Mg—In oxide film and the protective layer, as the linearexpansion coefficient of the protective layer of each field-effecttransistor of Comparative Examples 2 to 4 was small, i.e., 5×10⁻⁷ to20×10⁻⁷, compared to the linear expansion coefficient of the Mo film orMg—In oxide (In₂MgO₄) film, which was about 30×10⁻⁷.

Compared to the above, the protective layers of the field-effecttransistors of Examples 1 to 18 had the dielectric constant of 7.0 orlower due to the composition thereof, but had the linear expansioncoefficient of 30.0×10⁻⁷ or greater, and had no pealing and exhibitedexcellent results. Especially, the protective layers of the field-effecttransistors of Examples 1 to 3, 5 to 14, and 16 to 18 had the dielectricconstant of 6.0 or lower, and the linear expansion coefficient of30.0×10⁻⁷ to 60.0×10⁻⁷, and exhibited more excellent results.

Moreover, no pealing was observed on the protective layer of thefield-effect transistor produced in Comparative Example 1.

<Evaluation of Reliability of Properties of Transistor>

A DC bias stress test was performed in the N2 atmosphere on each of thefield-effect transistors produced in Examples 1 to 18, and ComparativeExample 1 for 160 hours.

Specifically, two types of the stress conditions were provided.

(1) Conditions including voltage between the gate electrode 22 and thesource electrode 24 (Vgs) being +20 V (Vgs=+20 V), and the voltagebetween the drain electrode 25 and the source electrode 24 (Vds) being 0V (Vds=0 V)

(2) Conditions including Vgs=Vds=+20 V

The result of the field-effect transistor produced in Example 1 with thestress conditions of Vgs=+20, and Vds=0V is presented in FIG. 11, andthe result thereof with the stress condition of Vgs=Vds=+20 is presentedin FIG. 12. Moreover, the result of the field-effect transistor producedin Comparative Example 1 with the stress conditions of Vgs=+20, andVds=0V is presented in FIG. 13, and the result thereof with the stresscondition of Vgs=Vds=+20 is presented in FIG. 14. In the graphs of FIGS.11 to 14, “E” on the vertical axis represents exponent of 10. Forexample, “1.E-03” represents “1×10⁻³” and “0.001,” and “LE-05”represents “1×10⁻⁵” and “0.00001.”

The onset voltage (Von) of the transistor properties was determined asthe voltage that was just below the voltage at which Ids exceeded 10⁻¹¹A in the course of increasing the Vg from −20 V stepwise by 0.5 V.

Paying attention to the sift amount ΔVon of the onset voltage Von duringthe stress test of 160 hours, the sift amount ΔVon was +8.0 V in thegraph of FIG. 13 and that was +7.5 V was in the graph of FIG. 14,whereas the sift amount ΔVon was +1.0 V in FIG. 11, and that was +1.5 Vin FIG. 12. The results of ΔVon from the stress test of 160 hoursperformed on the field-effect transistors produced in Examples 1 to 16,and Comparative Example 1 are presented in Table 16. It was confirmedfrom Table 16 that there was predominant difference between Examples 1to 18 and Comparative Example 1. Specifically, it was found that theprotective layers of the field-effect transistors produced in Examples 1to 18 were more suitable as a protective layer of a semiconductor layer(specially an oxide semiconductor layer) than that of the field-effecttransistor produced in Comparative Example 1.

Moreover, the field-effect transistors produced in Examples 1 to 18exhibited excellent reliability even in the atmosphere.

TABLE 16 Reliability evaluation of field-effect transistor ΔVon (V) Vgs= 20 V, Vds = 0 V Vgs = Vds = 20 V Ex. 1 +1.0 +1.5 Ex. 2 0 +1.0 Ex. 3 0+0.5 Ex. 4 +0.5 +0.5 Ex. 5 +0.5 +1.0 Ex. 6 0 +0.5 Ex. 7 0 +0.5 Ex. 8+0.5 +0.5 Ex. 9 0 +1.0 Ex. 10 +0.5 +0.5 Ex. 11 +1.0 +1.0 Ex. 12 +0.5+1.0 Ex. 13 0 +0.5 Ex. 14 +0.5 +0.5 Ex. 15 +0.5 +1.0 Ex. 16 0 +0.5 Ex.17 +1.0 +1.0 Ex. 18 +1.0 +0.5 Comp. +8.0 +7.5 Ex. 1

Example 19 <Production of Organic EL Display Device>

An organic EL display device as illustrated in FIG. 15 was produced.

—Formation of Gate Electrode—

First, a first gate electrode 52 and a second gate electrode 53 wereformed on a glass substrate 51. Specifically, an ITO film, which was atransparent electroconductive film, was formed on the glass substrate 51by DC sputtering so that the average film thickness of the ITO film wasto be about 100 nm. Thereafter, a photoresist was applied thereon, andthe applied photoresist was subjected to prebaking, light exposure by anexposure device, and developing, to thereby form a resist pattern thatwas identical to the pattern of the first gate electrode 52 and secondgate electrode 53 to be formed. The region of the ITO film, on which theresist pattern had not been formed, was removed by RIE. Thereafter, theresist pattern was removed, to thereby form the first gate electrode 52and the second gate electrode 53.

—Formation of Gate Insulating Layer—

Next, a gate insulating layer 54 was formed. Specifically, an Al₂O₃ filmwas formed above the first gate electrode 52, the second gate electrode53, and the glass substrate 51 by RF sputtering so that the average filmthickness of the Al₂O₃ film was to be about 300 nm. Thereafter, aphotoresist was applied thereon, and the applied photoresist wassubjected to prebaking, light exposure by an exposure device, anddeveloping, to thereby form a resist pattern, which was identical to thepattern of the gate insulating layer 54 to be formed. The region of theAl₂O₃ film, on which the resist pattern had not been formed, wasremoved, followed by removing the resist pattern, to thereby form thegate insulating layer 54.

—Formation of Source Electrode and Drain Electrode—

Next, a first source electrode 55 and a second source electrode 57, anda first drain electrode 56 and a second drain electrode 58 were formed.Specifically, an ITO film, which was a transparent electroconductivefilm, was formed on the gate insulating layer 54 by DC sputtering sothat the average film thickness of the ITO film was to be about 100 nm.Thereafter, a photoresist was applied on the ITO film, and the appliedphotoresist was subjected to prebaking, light exposure by an exposuredevice, and developing, to thereby form a resist pattern, which wasidentical to the pattern of the first source electrode 55 and the secondsource electrode 57, and first drain electrode 56 and the second drainelectrode 58 to be formed. The region of the ITO film, on which theresist pattern had not been formed, was removed by RIE. Thereafter, theresist pattern was removed, to thereby form the first source electrode55 and the second source electrode 57, and the first drain electrode 56and the second drain electrode 58, each of which was formed of the ITOfilm.

—Formation of Oxide Semiconductor Layer—

Next, a first oxide semiconductor layer 59 and a second oxidesemiconductor layer 60 were formed. Specifically, a Mg—In oxide(In₂MgO₄) film was formed by DC sputtering so that the average filmthickness thereof was to be about 100 nm. Thereafter, a photoresist wasapplied on the Mg—In oxide film, and the applied photoresist wassubjected to prebaking, light exposure by an exposure device, anddeveloping, to thereby form a resist pattern, which was identical to thepattern of the first oxide semiconductor layer 59 and the second oxidesemiconductor layer 60 to be formed. The region of the Mg—In oxide film,on which the resist pattern had not been formed, was removed by RIE.Thereafter, the resist pattern was removed, to thereby form the firstoxide semiconductor layer 59 and second oxide semiconductor layer 60. Inthe manner as described, the first oxide semiconductor layer 59 wasformed so that a channel was formed between the first source electrode55 and the first drain electrode 56. Moreover, the second oxidesemiconductor layer 60 was formed so that a channel was formed betweenthe second source electrode 57 and the second drain electrode 58.

—Formation of Protective Layer—

Next, a first protective layer 61 and a second protective layer 62 wereformed.

First, according to the amounts in Example 1 as depicted in Table 1,tetrabutoxy silane (T5702-100G, of Aldrich), aluminumdi(s-butoxide)acetoacetic acid ester chelate (Al content: 8.4%, Alfa89349, of Alfa Aesar), triisopropyl borate (Wako 320-41532, manufacturedby Wako Chemical Ltd.), a calcium 2-ethylhexanoate mineral spiritssolution (Ca content: 5%, 351-01162, manufactured by Wako ChemicalLtd.), and a strontium 2-ethylhexanoate toluene solution (Sr content:2%, 195-09561, manufactured by Wako Pure Chemical Industries, Ltd.) werediluted with mesitylene, to thereby form a coating liquid for forming aprotective layer. The metal oxide formed by the coating liquid forforming the protective layer had the same composition to that of Example1 depicted in Table 2.

The coating liquid for forming the protective layer was applied byinkjet printing to thereby form a protective layer so that theprotective layer covered the first oxide semiconductor layer 59 and thesecond oxide semiconductor layer 60. After drying the protective layerat 120° C. for 1 hour, baking was performed in the 02 atmosphere at 400°C. for 3 hours. As a result, a SiO₂-A₂O₃—B₂O₃—CaO—SrO metal oxidecomposite insulating film (protective layer) was obtained as the firstprotective layer 61 and the second protective layer 62. The average filmthickness of the first protective layer 61 and the second protectivelayer 62 was about 30 nm. —Formation of Interlayer Insulating Film—

Next, an interlayer insulating film 63 was formed. Specifically, apositive photosensitive organic material (SUMIRESIN EXCEL CRC series,manufactured by Sumitomo Bakelite Co., Ltd.) was applied by spincoating, followed by subjecting to prebaking, light exposure by anexposure device, and developing, to thereby obtain the desired pattern.Thereafter, the resultant was subjected to post baking at 320° C. for 30minutes, to thereby form the interlayer insulating film 63 having athrough-hole above the second drain electrode 58. The interlayerinsulating film 63 formed in this manner had the average film thicknessof about 3 μm. No pealing was observed on the protective layers 61 and62 even after the post baling of the interlayer insulating film 63.

—Formation of Partition Wall—

Next, a partition wall 64 was formed. Specifically, a surfacemodification of the interlayer insulating film 63 was performed by a UVozone treatment. Thereafter, a positive photosensitive polyimide resin(DL-1000, manufactured by Toray Industries, Inc.) was applied thereon byspin coating, and the applied resin was subjected to prebaking, lightexposure by an exposure device, and developing, to thereby obtain thedesired pattern. Thereafter, the obtained pattern was subjected to postbaking at 230° C. for 30 minutes, to thereby form a partition wall 64.

—Formation of Positive Electrode—

Next, a positive electrode 65 was formed. Specifically, a surfacemodification of the interlayer insulating film 63 was again performed bya UV ozone treatment, followed by applying an ITO ink containing nanoparticles thereon through inkjet printing, to thereby form the positiveelectrode 65 having the average film thickness of about 50 nm.

—Formation of Organic EL Layer—

Next, an organic El layer 66 was formed on the positive electrode 65using a polymeric organic luminescent material by means of an inkjetdevice.

—Formation of Negative Electrode—

Next, a negative electrode 67 was formed. Specifically, the negativeelectrode 67 was formed by vacuum depositing MgAg on the organic ELlayer 66 and the partition wall 64.

—Formation of Sealing Layer—

Next, a sealing layer 68 was formed. Specifically, a SiNx film wasformed by PECVD so that the average film thickness thereof was to beabout 2 μm, to thereby form the sealing layer 68 on the negativeelectrode 67.

—Bonding—

Next, the resultant was bonded to a counter substrate 70. Specifically,an adhesive layer 69 was formed on the sealing layer 68, and the countersubstrate 70 composed of a glass substrate was bonded thereon. In thismanner as described, a display panel of the organic EL display devicehaving the structure illustrated in FIG. 15 was produced.

—Connection of Driving Circuit—

Next, a driving circuit was connected. Specifically, the driving circuit(not illustrated) was connected to the display panel so that an imagecould be displayed on the display panel. In the manner as described, animage display system of the organic EL display device was produced.

This organic EL display device is so-called “bottom emission” organic ELdisplay device, as the field-effect transistor is all composed oftransparent films, and a metal layer having high reflectance is usedonly for the negative electrode.

This organic EL display element exhibited high-speed operation and highreliability.

The embodiments of the present invention are, for example, as follows:

<1> A field-effect transistor, containing:

a substrate;

a protective layer;

a gate insulating layer formed between the substrate and the protectivelayer;

a source electrode and a drain electrode, which are formed to be incontact with the gate insulating layer;

a semiconductor layer, which is formed at least between the sourceelectrode and the drain electrode, and is in contact with the gateinsulating layer, the source electrode, and the drain electrode; and

a gate electrode, which is formed at an opposite side to the side wherethe semiconductor layer is provided, with the gate insulating layerbeing between the gate electrode and the semiconductor layer, and is incontact with the gate insulating layer,

wherein the protective layer contains a metal oxide composite, whichcontains at least Si and alkaline earth metal.

<2> The field-effect transistor according to <1>, wherein the metaloxide composite further contains Al, or B, or a combination of Al and B.<3> The field-effect transistor according to any of <1> or <2>, whereinthe semiconductor layer is an oxide semiconductor layer.<4> The field-effect transistor according to any one of <1> to <3>,wherein the alkaline earth metal is at least one selected from the groupconsisting of Mg, Ca, Sr, and Ba.<5> A display element, containing:

an optical control element configured to control optical outputcorresponding to a driving signal; and

a driving circuit, which contains the field-effect transistor accordingto any one of <1> to <4>, and is configured to drive the optical controlelement.

<6> The display element according to <5>, wherein the optical controlelement contains an electroluminescent element, an electrochromicelement, a liquid crystal element, an electrophoretic element, or anelectrowetting element.<7> An image display device, which displays an image corresponding toimage data, the image display device containing:

a plurality of the display elements each according to any of <5> or <6>,which are arranged in a matrix;

a plurality of lines configured to separately apply gate voltage to eachfield-effect transistor in each display element; and

a display control device configured to individually control the gatevoltage of each field-effect transistor through the lines, correspondingto the image data.

<8> A system, containing:

the image display device according to <7>; and

an image data forming device configured to form image data based uponimage information to be displayed, and to output the image data to theimage display device.

REFERENCE SIGNS LIST

-   -   11 field-effect transistor    -   12 field-effect transistor    -   13 capacitor    -   14 field-effect transistor    -   15 capacitor    -   16 counter electrode    -   21 substrate    -   22 gate electrode    -   23 gate insulating layer    -   24 source electrode    -   25 drain electrode    -   26 oxide semiconductor layer    -   27 protective layer    -   31 substrate    -   32 first gate electrode    -   33 second gate electrode    -   34 gate insulating layer    -   35 first source electrode    -   36 second source electrode    -   37 first drain electrode    -   38 second drain electrode    -   39 first oxide semiconductor layer    -   40 second oxide semiconductor layer    -   41 first protective layer    -   42 second protective layer    -   43 interlayer insulating film    -   44 organic EL layer    -   45 negative electrode    -   51 glass substrate    -   52 first gate electrode    -   53 second gate electrode    -   54 gate insulating layer    -   55 first source electrode    -   56 first drain electrode    -   57 second source electrode    -   58 second drain electrode    -   59 first oxide semiconductor layer    -   60 second oxide semiconductor layer    -   61 first protective layer    -   62 first protective layer    -   63 interlayer insulating film    -   64 partition wall    -   65 positive electrode    -   66 organic EL layer    -   67 negative electrode    -   68 sealing layer    -   69 adhesive layer    -   70 counter substrate    -   81 glass substrate    -   82 lower electrode    -   83 dielectric layer    -   84 upper electrode    -   302, 302′ display element    -   310 display    -   312 negative electrode    -   314 positive electrode    -   320, 320′ driving circuit    -   340 organic EL thin film layer    -   342 electron transporting layer    -   344 light emitting layer    -   346 hole transporting layer    -   350 organic EL element    -   370 liquid crystal element    -   372 counter electrode    -   400 display control device    -   402 image data processing circuit    -   404 scanning line driving circuit    -   406 data line driving circuit

What is claimed:
 1. A coating liquid for forming insulating filmcomprising: a silicon-containing compound, an inorganic alkaline earthmetal compound (except for calcium carbonate, magnesium carbonate,barium sulfate, and calcium sulfate), and a solvent.
 2. The coatingliquid for forming insulating film according to claim 1, wherein theinorganic alkaline earth metal compound is at least any one of alkalineearth metal nitric acid salt, alkaline earth metal chloride, alkalineearth metal fluoride, alkaline earth metal bromide, alkaline earth metaliodide.
 3. A coating liquid for forming insulating film comprising: asilicon-containing compound, an organic alkaline earth metal compound,and a solvent, wherein the organic alkaline earth metal-containingcompound comprises at least any one of acyloxy group, a phenyl group, anacetylacetonato group, and a sulfonic acid group.
 4. The coating liquidfor forming insulating film according to claim 1, further comprising atleast any one of an aluminum-containing compound, and a boron-containingcompound.
 5. A coating liquid for forming insulating film comprising asilicon-containing compound, an alkaline earth metal-containingcompound, at least any one of an inorganic aluminum compound and aninorganic boron compound, and a solvent.
 6. A coating liquid for forminginsulating film comprising a silicon-containing compound, an alkalineearth metal-containing compound, at least any one of an organic aluminumcompound and an organic boron compound, and a solvent, wherein theorganic aluminum compound comprises at least any one of acyloxy group,an acetylacetonato group, and a sulfonic acid group, and wherein theorganic boron compound comprises at least any one of triethyl borane,(R)-5,5-diphenyl-2-methyl-3,4-propano-1,3,2-oxazaborolidine,2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane,bis(hexyleneglycolato)diboron,4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazole,tert-butyl-N-[4-(4,4,5,5-tetramethyl-1,2,3-dioxaborolan-2-yl)phenyl]carbamate,phenyl boronic acid, 3-acetylphenyl boronic acid, boron trifluorideacetic acid complex, boron trifluoride sulfolane complex, 2-thiopheneboronic acid, and tris(trimethylsilyl) borate.
 7. A coating liquid forforming insulating film comprising: a silicon-containing compound, analkaline earth metal-containing compound, at least any one of an organicaluminum compound and an organic boron compound, and a solvent, whereinthe organic aluminum compound comprises at least any one of acyloxygroup, an acetylacetonato group, and a sulfonic acid group, and whereinthe organic boron compound comprises at least any one of acyloxy group,a phenyl group, a sulfonic acid group, and a thiophene group.